Century: Age of Ashes is a free-to-play multiplayer game that lets players fly around on dragons and battle other dragon riders. It has a competitive design, and players can level up their profile level. This is the primary way to unlock new cosmetics, so players will want to level up quickly if they want to customize their characters and dragons.
To level up quickly in Century: Age of Ashes, players can use XP boosts and complete missions. You can find your current missions and how experience they give you on the right side of the home screen. XP boosts can be found in the bottom-right corner of that same screen.
You can purchase XP boosts in the store. Using this will increase the amount of experience you receive at the end of a match. You can see how much experience you receive after a match. This is calculated based on your performance, any active boosters, and completed missions.
Leveling up will be the primary way you earn cosmetics and how you get rewards. Targeting these missions and using boosters will let you level up quickly and earn more rewards.
For more information on Century: Age of Ashes, check out Does Century: Age of Ashes have controller support? and Are they dragons or wyverns in Century: Age of Ashes on Pro Game Guides.